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    <meta charset="UTF-8">
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    <title>Document</title>
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<body>
    <script>
        // typeof  
        // 可以看见 null 数组 跟{}对象 都是object 是无法区分的
        console.log(typeof ""); // string

        console.log(typeof 1); // number

        console.log(typeof true); // boolean

        console.log(typeof undefined); // undefined

        console.log(typeof null); // object

        console.log(typeof {}); // object

        console.log(typeof []); //  object

        console.log(typeof
            function () {}); // function.
    </script>
    
</body>

</html>